This invention relates to a general service incandescent lamp having an inner envelope serving as its main light source. More particularly, this invention relates to a three (3)-way incandescent lamp having a tungsten halogen-cycle inner envelope and an operating circuit for the inner envelope all lodged within the confines of the lamp itself.
Inner envelopes containing a tungsten filament along with a halogen additive have recently been employed in automotive headlamps and PAR lamps. The tungsten halogen-cycle inner envelope provides for an enhanced light source for the lamps in which they are employed.
The usage of a tungsten halogen-cycle inner envelope for incandescent lamps such as a three (3)-way incandescent lamp is desired. The typical three (3)-way incandescent lamp has low and high wattage type filaments supplying three different levels of illumination. The usage of two tungsten halogen-cycle inner envelopes to respectively replace the low and high wattage filaments is neither economically nor structurally advantageous. The placement of two separate tungsten halogen-cycle inner envelopes within the confines of the outer envelope of the lamp complicates the mounting structure and adds to the cost of the lamp. It is desired that a single tungsten halogen-cycle inner envelope be lodged within the incandescent lamp and operated so as to provide three different levels of illumination for the lamp.
The selection of the three levels of illumination must be carefully considered so as to take into account the range of operating parameters of the halogen-cycle inner envelope. It must be recognized that there is a limit to the range of operation of a tungsten halogen-cycle lamp, the effect of which is to limit the difference in possible levels of illumination for the lamp. If, for example, the lower illumination level is chosen so that the inner wall of the inner envelope is operated below a desired temperature, then the halogen cycle may not function properly possibly resulting in wall blackening and the halogen detrimentally and chemically attacking the filament and support members of the inner envelope. Selection of the desired illumination levels of the inner envelope must be accomplished in a predetermined manner so as to ensure obtainment of the desired performance of the lamp itself.
A single inner envelope having a single tungsten filament operated at three levels of illumination necessitates that a ballast or operating circuit be provided for the lamp. A ballast or operating circuit that allows a lamp having a single filament to be operated to provide three levels of illumination is commercially available from I. Q. Industries, Inc., of Cleveland, Ohio 44118 as their CONVERT-A-BULB.TM. product. The CONVERT-A-BULB product has a housing large enough for lodging the operating circuit, a male connector for inserting into a three-way socket of a lamp fixture and a female connector for accepting a medium screw-type base of the lamp having the single filament.
It is desired that the operating circuit for the single tungsten filament lodged within an inner envelope containing halogen be lodged within a medium screw-type base of the lamp itself and that the operating circuit provide the lamp with three different levels of illumination that are selected in accordance with the desired parameters of the tungsten-halogen inner envelope.
Accordingly, it is an object of the present invention to provide a three (3)-way incandescent lamp having an operating circuit lodged within the confines of the lamp itself and which operating circuit provides for three levels of illumination of the tungsten halogen-cycle inner envelope so as to provide the lamp with an enhanced and properly operated light source.